invoke_noreturn_cold

Summary:
[Folly] `invoke_noreturn_cold`, a helper function for invoking another function with arguments in a `[[noreturn]]` and `[[gnu::cold]]` context.

Potentially useful for making the bytecode at the call-site small for icache size or always-inlined fast-path size concerns, when constructing the exception object to be thrown is more complex than passing pre-existing values by reference, such as when computing a message is required.

Reviewed By: marshallcline

Differential Revision: D9509658

fbshipit-source-id: b8272629876f9e7e81ae0f7a7f06404484d297f2

folly/lang/Exception.h

@@ -92,4 +92,36 @@ terminate_with(Args&&... args) noexcept {
 }
 // clang-format on
 
+/// invoke_noreturn_cold
+///
+/// Invoke the provided function with the provided arguments. If the invocation
+/// returns, terminate.
+///
+/// May be used with throw_exception in cases where construction of the object
+/// to be thrown requires more than just invoking its constructor with a given
+/// sequence of arguments passed by reference - for example, if a string message
+/// must be computed before being passed to the constructor of the object to be
+/// thrown.
+///
+/// Usage note:
+/// Passing extra values as arguments rather than capturing them allows smaller
+/// bytecode at the call-site.
+///
+/// Example:
+///
+///   if (i < 0) {
+///     invoke_noreturn_cold(
+///         [](int j) {
+///           throw_exceptions(runtime_error(to<string>("invalid: ", j)));
+///         },
+///         i);
+///   }
+template <typename F, typename... A>
+[[noreturn]] FOLLY_NOINLINE FOLLY_COLD void invoke_noreturn_cold(
+    F&& f,
+    A&&... a) {
+  static_cast<F&&>(f)(static_cast<A&&>(a)...);
+  std::terminate();
+}
+
 } // namespace folly

folly/lang/test/ExceptionTest.cpp

@@ -48,6 +48,15 @@ static std::string message_for_terminate_with(std::string const& what) {
   // clang-format on
 }
 
+static std::string message_for_terminate() {
+  // clang-format off
+  return
+      folly::kIsGlibcxx ? "terminate called without an active exception" :
+      folly::kIsLibcpp ? "terminating" :
+      "" /* empty regex matches anything */;
+  // clang-format on
+}
+
 class MyException : public std::exception {
  private:
   char const* what_;
@@ -93,3 +102,10 @@ TEST_F(ExceptionTest, terminate_with_variadic) {
       folly::terminate_with<MyException>("hello world", 6),
       message_for_terminate_with<MyException>("world"));
 }
+
+TEST_F(ExceptionTest, invoke_noreturn_cold) {
+  EXPECT_THROW(
+      folly::invoke_noreturn_cold([] { throw std::runtime_error("bad"); }),
+      std::runtime_error);
+  EXPECT_DEATH(folly::invoke_noreturn_cold([] {}), message_for_terminate());
+}